<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>
<script type="text/javascript">
	
	var a = '123';
	var b = a;
	var c = b;
	var d = c;
	a.concat(d);
	b.concat(a);
	alert(a); //'123'
	alert(b); //'123'
	alert(c); //'123'
	alert(a,b,c,d);//'123'


</script>
</body>
</html>